Method and apparatus for controlling arc lamps



Feb. 2, 1937. R 5 WILSON 2,069,597

METHOD AND APPARATUS FOR CONTROLLING ARC LAMPS Filed Oct. 9, 1933 Patented Feb. 2, 1937 IMETHOD AND APPARATUS FOR CONTROILING ARC LAWS Russell E. Wilson, Cleveland, Ohio Application October 9,

6 Claims.

My invention relates to a method and apparatus for maintaining constant color and brllliancy of light in arc lamps, and is especially adapted for use in connection with projectors that are used in motion picture theatres.

Experience has shown that while the present low intensity direct-current projection are when viewed by itself apparently gives a brilliant white light, nevertheless when compared with that 10 which is obtained from a high intensity are, it is yellowish white in color. Considerable research work therefore, has been undertaken to develop an alternating current projection arc to bridge the present wide gap in effective screen illumina- 18 tion that exists between the high intensity arc,

which is used by the larger theatres, and the low intensity direct current arc, which is generally in use by the small theatres. The purpose of such research work has been to give the smaller theatres the same advantage of a blue white light for screen illumination, which has been available for use only to the larger theatres, and

which is so desirable for the use of colored films.

The research referred to has resulted in the development of an electrode, which has not only produced a marked improvement in color and brilliancy of light by the use of alternating current, but has resulted in other economical advantages. For example, the power required to produce a given screen illumination with the new are is less than that of the low intensity direct current arc. Moreover, by means of the use of a specially designed transformer, which is comparatively low in cost, there is eliminated the use of motor-generator sets, rectifier-s, converters, and the power-consuming ballast resistances, which are now required with the direct-current projection equipment. Thus, adequate screen illumination is made available tov all theatres in districts, where alternating-current only is available.

By means of the new electrode, it has been possible to effect an increase in arc current with a decreased arc voltage, thereby concentrating the light giving power of the are into a much smaller volume near the electrode tips than has heretofore been possible. Such concentration of power in a small surface or space enables it to be focused easily by means of a mirror. The

1933, Serial No. 692,855

electrodes would possess no practical utility unless they could be fed automatically at the required rate. Experience has shown that even a slight deviation from the feeding rate would cause a rapid variation in the flow of current, and thus modify the color of the light.

An object of my invention therefore, is to provide a method and apparatus for automatically controlling the feeding of the electrodes, so as to maintain constant intensity of illumination regardless of the variable rate at which the electrodes may burn. An additional object is to provide apparatus, which may readily be used in combination with existing equipment without considerable modification in the construction thereof. Thus, I have made available for use in all, localities, a source of light, which at present is available only to the larger theatres, which are able to purchase and maintain expensive equipment.

In the drawing, Fig. l is a side elevation of a projector with which my invention is adapted to be used; Fig. 2 is a side elevation partly in section of the photo-electric detection apparatus; Fig. 3 is a section taken on the line 33 in Fig. 2; Fig. i is a wiring diagram, and Fig. 5 is a side elevation of a modified form of the photo-electric detection apparatus.

The preferred method of accomplishing my invention is to utilize the variation in the electrical characteristics of the current, which is flowing across the gap between the electrodes for operating a feeding apparatus. The method, which I have illustrated in the drawing includes a photo-electric cell, which is utilized for controlling an electric circuit that operates the feeding apparatus. The cell in turn is energized by a source of light, which may be either the light of the are or an outside source of supply. The means for controlling the impingement of light upon the cell may be the pointer of an ammeter or voltmeter, which is connected in series with the electrodes. I have found that such method maintains the desired blue-white intensity automatically with a variation of only one ampere across the gap.

Referring now more particularly to the drawing, I0 indicates a projector in which are shown electrodes II, that are held in arms Ill. The arms may be movably mounted relatively to each other upon a right and left hand threaded screw shaft l3, and the shaft in turn may be rotated through suitable reduction gearing by an electric motor ll.

A meter, such as an ammeter having a. pointer I6 is connected in series with the electrodes. I

- utilize the movement of the pointer to vary the are or from a lamp I9. In the case of an outside source of light, the apparatus may be placed in a position remote from the projector, thereby allowing ample space adjacent the projector for the operator. I

When the arc is struck, the electrodes are manually adjusted to the proper position to obtain the most efficient operation. In practice, the beam of light and the cell are positioned about one ampere below that which is desired for most eflicient operation. As the electrodes burn, the amperage decreases, and the pointer moves back until it shuts off the light from the cell. The cell relay 20 is normally closed when the cell is not energized by light, and is in circuit with a second normally open relay 2|, which controls the operation of the motor, as is shown in Fig. 4. The arrangement is such that when the light strikes the cell, the motor is stopped, and when the pointer is interposed in the path of the beam of light, the motor is started. When the motor operates, the electrodes. are fed closer together, the amperage across the gap increases, the pointer swings out of the path of the light, thus uncovering the cell, and the cell circuit is thereby energized to open the motor circuit. The electrodes then continue to burn, and the amperage drops until the pointer again cuts off thebeam of light. Thus, the motor is automatically operated to maintain a feeding rate that is substantially synchronized with the burning rate. The mechanism is so sensitive in operation that the amperage can be maintained substantially constant with a variation of only one-half to one ampere. In this way,'a blue-white light is constantly and automatically maintained.

The apparatus which I have illustrated and described is adapted for maintaining aconstant flow of current at selective rates. To this end, I have shown the ammeter, as being oscillatably mounted upon a pivot 40, and I have shown a suitable mechanism for moving the ammeter with reference to the pivot. One form of such mechanism comprises a worm 4| which is adapted to mesh with a gear segment 42 that is attached to the ammeter casing. The worm shaft, in turn, is journalled in a fixed support and is adapted to be manually rotated.

A modification of my invention is illustrated in Fig. 5 wherein the beam of light is directed downwardly acrossthe face of the ammeter and wherein the device for interrupting the beam either forms part of the pointer, which is extended at right angles to the normal direction of it, or embodies a light plate that is carried by the ammeter and that extends in a plane at right angles to the plane of the pointer. The advantage of this modified arrangement is that a slot need not be cut in the face of the ammeter, and that the entire assembly may be mounted in a compact housing.

From the foregoing description, it will be apparent that I have provided a method and apparatus that can be readily used in connection with present projector equipment and that operates satisfactorily with alternating current to mainain constant blue-white light of uniform bril liancy.

I claim:

1. An apparatus for controlling the position of the electrodes in an arclamp comprising in combination, an electric motor for feeding the electrodes, an ammeter in circuit with the electrodes and having a pointer, and a photo-electric detection device actuated by movement of the pointer for operating said motor to maintain a feeding rate that is substantially synchronized with the burning rate of the electrodes.

2. An apparatus for controlling the position of the electrodes in an arc lamp, comprising in combination an electrode feeding device, an electric meter in circuit with the electrodes, and having a pointer, and a photo-electric detection device independent of the arc lamp coacting with the pointer and influenced by the movements of the pointer for actuating an electrode feeding device to maintain a feeding rate, which is substantially synchronized with the burning rate.

3. An apparatus for controlling the feeding of electrodes in an arc lamp comprising a photoelectric detection device, a meter in circuit with the electrodes whose fluctuations control the detection device, the meter being pivotally supported, and means for manually swinging the meter about its pivot so as to set the apparatus for maintaining the arc current at any given predetermined degree.

4. A method of maintaining substantially uniform color' and brilliancy of light in an arc lamp comprising, causing a part of a current responsive device to move in accordance with variations in the current strength of the current flowing across. the arc, utilizing the movements of such part to interrupt a beam of light that is normally directed upon a photo-electric cell, so as to give total light or darkness to the cell and utilizing the shadow that is cast by said part upon the cell for controlling the apparatus that moves the electrodes.

5. A method of synchronizing the feeding of electrodes in an arc lamp with the burning rate, comprising movin g a pointer on a current responsive member in accordance with the variations in the current strength of the current flowing across the arc, utilizing the opaque characteristics of the pointer for totally obstructing a beam of light or allowing full intensity, then using the variations in the shadow that is cast by the pointer for varying the resistance in an electric circuit and employing the current in the circuit to actuate an electrode feeding apparatus.

6. An apparatus for feeding the electrodes of an arc lamp comprising in combination a circuit for the lamps, an electric motor; mechanism operated by the motor for feeding the electrodes, a meter in series with the arc circuit and having a movable pointer, a source of light, a photoelectric cell spaced from the light, the pointer being normally out of the path of light allowing full intensity in the cell when the current is flowing across the are at the desired rate, and being movable into the path causing the cell to be dark when the current drops from the normal degree, a circuit having a relay therein for the cell, and means actuated by the relay for controlling the motor circuit.

RUSSELL E. WILSON. 

